Optical wavelengths are typically referred to as radiation encompassing UV, visible and infra-red wavelengths of about 200 nm to 25,000 nm. Solar radiation on earth's surface is generally between 290 nm and 2500 nm. Chromogenic devices for optical attenuation are of several kinds, such as liquid crystal devices, suspended particle devices, user controllable photochromic devices and electrochromic (EC) devices (e.g., see WO 98/08137 for a description of such devices and the various kinds of electrochromic devices the complete disclosure of which is incorporated by reference herein). All further discussions will be limited to the EC devices, although anyone familiar with art can extend the principles of the disclosure here to the other chromogenic devices as well. EC devices have several advantages, wide spectral response, wider temperature capability, generally non-polarizing attenuation, angle independent contrast, possibility of larger size scale-up, etc. The applications described below are discrete, however, many of the elements and concepts described here for one application may apply to the others as well. In addition, many EC materials may change electrical and magnetic properties, and this change can be used to change transmission of non-optical radiation such as radio and microwaves.
FIGS. 1a and 1b show examples of typical electrochromic device fabricated using two substrates, however many other EC devices can be fabricated, some of them may only use one substrate.
FIG. 1a shows two substrates 120 and 121. These have conductive coatings 130 and 131, respectively. An EC layer 140 is deposited on 131. The two substrates are connected using an electrolyte 150. The edges of the device are sealed using a sealant 170 to protect the inside of the device, and also to contain the electrolytic components. Power is applied through the connectors 110 and 111 to change the optical density. A DC voltage, typically less than 5 volts is applied across the connectors to color the device. The ions are either inserted or expelled from the EC layer that causes a change in color. A corresponding reaction takes place at the interface of the electrolyte and the other electrode involving the redox species which is incorporated in the electrolyte.
When the voltage is removed or reversed, the reactions also reverse.
FIG. 1b shows another type of EC device which has a counterelectrode (ion storage layer) 160 deposited on a conductive coating 132 which is pre-deposited on a substrate 123. The other substrate 122 is coated with a conductive coating 133 and then with an EC layer 141. They are connected together by an electrolyte 151 and sealed at the edges by a sealant 171. Power is applied via the connectors 112 and 113. In the bleached state the ions such as protons, lithium and sodium reside in the counter-electrode. Under an appropriate voltage, these ions are reversibly extracted from the counterelectrode, travel through the electrolyte and are then inserted in the EC layer. This causes a change in transmission, i.e., coloration in the EC layer assuming that the EC layer is cathodically electrochromic. There may also be a simultaneous change in the optical transmission of the counter electrode by expulsion of ions if it is anodically electrochromic.
Transparent means substrates which transmit part of the electromagnetic radiation which is being modulated by the device. Examples of transmissive substrates are glass, plastics, silicon, etc. Some examples of transparent electrical conductors are coatings based on thin metal layers such as gold, palladium, rhodium, alloys and doped oxides such as tin oxide, indium oxide, zinc oxide and antimony oxide, and some of the preferred dopants in each of these oxides are fluorine, tin oxide, aluminum oxide and tin oxide respectively. The dopants may be present up to 25% concentrations (measured as atomic ratio of dopant to host cations). The thickness of the oxide coatings is typically between 10 nm to 10,000 nm. For metallic coatings the upper limit is around 30-50 nm before they become optically opaque. There may be other layers below the transparent conductors, such as anti-iridescent layers, dielectrics, other metals, etc. Examples of EC materials are tungsten oxide, molybdenum oxide, iridium oxide, nickel oxide, polythiophene and polyaniline. Typical thickness of EC layer is in the range of 10 nm to about a 1000 nm. The electrochromic cell is assembled with the coatings facing inwards. A predetermined distance separates the two substrates. This distance or the gap is filled with an electrolyte which could be a liquid or a solid. The edge of the device is sealed for example with an organic sealant (e.g., curable epoxy resin) or an inorganic sealant (e.g., solder glass) so that the interior of the device is protected from the environment and the electrolyte (if liquid) does not leak out. The electrolyte thickness or the gap between the two substrates can be controlled by the thickness of the solid electrolyte, spacers in the electrolyte and/or the seals. Typical gaps are in the range of 5 microns to 5000 microns, where gaps between 10 and 1000 microns are preferred.
The electrolyte in an electrochromic device in FIG. 1a will have at least one polar solvent, one dissociable salt and a redox promoter in the electrolyte. Sometimes the salt and the redox promoter may be combined into one such material as lithium iodide, viologen salt, etc. Examples of salts are NaCF3SO3, NH4BF4, LiClO4, LiASF6, LiBF4, LICF3SO3, Li N (CF3SO3)2. Examples of redox materials are LiI, Iodine, viologen salts, phenothiazine, metallocenes such as ferrocene and its derivatives. Examples of solvents are tetraglyme, propylene carbonate, ethylene carbonate, gamma-butyrolactone, sulfolane and its derivatives, acetonitrile and other nitrile solvents. Other additives such as UV stabilizers, fillers, opacifiers and viscosity modifiers may be used. Examples of UV stabilizers are benzophenones, benzotriazoles, metal complexes and combinations. Some commercial examples are Uvinul 3035, Uvinul 3000 from BASF (Mount Olive, N.J.), the same from Ciba Specialty Chemicals (Brewster, N.Y.) are Tinuvin 234 and from Cytec, West Paterson, N.J., Cyasorb UV1164. Some viscosity modifiers are polymers and copolymers of polypropylene oxide, polyethylene oxide, acrylics such as polymethylmethacrylate, and polyurethanes, etc. One may even have monomeric additives and catalysts that will polymerize in-situ to yield a solid polymer or a higher viscosity electrolyte. Some of these polymerize by addition polymerization such as acrylic or acrylate terminated groups with free radical or ionic initiators, or polycondensation such as isocyanates and hydroxy terminated groups with appropriate catalysts such as tin octoate, etc. Examples of components in such devices can be found in, e.g., U.S. Pat. Nos. 5,910,854 and 6,045,724.
In FIG. 1b the redox promoter in the electrolyte is not necessary as one of the EC or the ion-storage layer is intercalated with ions (typically protons, lithium, sodium, potassium, etc.) which are shuttled reversibly between the EC layer and the ion-storage layer. For an EC layer that colors upon reduction, these ions are inserted in this electrode for coloration and extracted for bleach. For anodic coloring EC layer the coloration occurs by expulsion of the ions and bleach by ion-intercalation. Also, in an EC device the EC layer could be a cathodically coloring layer such as tungsten oxide and molybdenum oxide and the ion-storage layer could also be an EC layer that colors anodically, such as polyaniline and nickel oxide. Also due to the insertion of ions in an electrode, refractive index changes are introduced, and these changes could also be used for changing the light propagation direction, hence switching.
In FIGS. 1a and 1b the two substrates are offset to facilitate an electrical connection to the conductive layers. One may even extended the conductive strip from the transparent conductor to the edge or the back side of substrate and then attach the connecting electrical wires, e.g., by soldering. The extension of conductive path on to the edges, etc., may be done using conductive solders, silver frits and conductive tapes.
An electrochromic device may be colored by varying the electric potential applied to one substrate relative to the second. Tungsten oxide exhibits broad absorption almost in the entire range of solar radiation. Electrochromic devices can also be formed on single substrates by sequentially depositing an electronic (or electrical) conductor coating (such as tin doped indium oxide (ITO), fluorine or antimony doped tin oxide, gold, rhodium), an ion-intercalative layer (such as tungsten oxide, molybdenum oxide, niobium oxide, titanium oxide), ion transport layer (such as tantalum oxide (proton conductor), lithium titanate. (lithium conductor), another ion intercalative layer (such as those described above and iridium oxide, nickel oxide, vanadium oxide, polyaniline) and finally another conductor coating (examples described above). At least one of these conductors is transparent and at least one of the ion-intercalative layer is electrochromic, i.e., changes its color reversibly upon ion insertion and ion extraction. All the materials described above may be alloyed or combined with other materials as described in the art. Further, for purposes of this invention where non optical electromagnetic spectrum has to be varied, the electrochromic property of a layer in any of the above devices will be extended in definition to include where the electrical conductivity of the EC layer will change reversibly upon ion insertion and ion extraction. Another kind of EC device will be included in this discussion where a metal (copper, bismuth, etc.) is reversibly deposited due to the electrochemical action on one of the electrodes, an example of this is in U.S. Pat. No. 5,903,382, which is incorporated by reference herein. In this invention the term switches, modulator and attenuators be will be used interchangeably as in a broader sense all of these imply where the intensity of the signal which passes through these is changed.